An evaluation of methods used by different river forecast centers to calculate reasonable maximum and reasonable minumum forecasts

This paper compares methods used by the different river forecast centers for calculating the reasonable maximum and reasonable minimum water supply forecasts. Five procedures used by different forecast centers were identified and evaluated. Results from using the five methods on common watersheds with the same prediction equations are summarized and compared for four forecast dates. Although each method purports to provide estimates of the reasonable maximum and reasonable minimum that would be exceeded only 10 percent of the time, or once every ten years, the actual return periods for the difference methods ranged from 3 years to over 500 years.